I would try to decide early on whether you are leaning plinker, hunting or home defense. Some options are just as well done at the factory as opposed to doing at home. No sense paying for a free float hand guard with rails every 60degrees if you plan on busting Pdogs or coyotes. As there is little sense laying a stock hand guard in a box in the basement if you know darned good and well you want a billet handguard with lots of rail surface right now. I have said it before and will say it again get the good trigger upgrade today because the stock one is a poor substitute for the one your Daisy Red Rider came with.
I would look at a flat top, and add Back Up Irons from day one, if you are going plinker / home defense. If a collapsable buttstock is a sure thing get one right now, if for no other reason than the buffer tube won't need replacement.
Or, and this is where I'm at. Buy a plain old AR-15 about as generic as you can find. At the same time have a complete lower sent. As you decide what you like and don't like build the lower to your spec's one piece at a time. In a year or so you can sell the original if it is so out of spec you have no further use for it. But if you decide you want a 6.8 dedicated hunting gun, but hate to give up a great range gun / defense / varmint rifle. You won't be lamenting the 5.56 and its stopping ability when hunting hogs and deer, or cringing at ammo costs at the range when having fun.
You will soon figure out why your sister needed so many Barbies. They really aren't the same thing to the trained observer.
